1
2 /**
3 * A Quack of objects
4 *
5 * This implementation uses linked memory
6 *
7 * @version 1.0
8 * @author Prof. David Bernstein, James Madison University
9 */
10 public class Quack
11 {
12 private Node first, last;
13
14
15 /**
16 * Construct a new (empty) Quack
17 */
18 public Quack()
19 {
20 first = null;
21 last = null;
22 }
23
24
25
26
27 /**
28 * Pep an Object off of this Quack
29 *
30 * @return The Object
31 */
32 public Object pep()
33 {
34 Node temp;
35 Object value;
36 value = null;
37
38 if (first != null) // if first is pointing somewhere
39 {
40 value = first.value;
41 if (first == last) // asks whether first is pointing where last is pointing
42 {
43 first = null; // make first point to null (point nowhere)
44 }
45 else
46 {
47 temp = last; // makes temp point where last is pointing
48 while (temp.next != first)
49 {
50 temp = temp.next; // makes temp point where temp.next is pointing
51 }
52 first = temp; // makes first point where temp is pointing
53 first.next = null; // makes first.next point to null
54 }
55 }
56
57 if (first == null) // if first is pointing to null ( point nowhere)

58 last = null; // make last point to null (point nowhere)
59 return value;
60 }
61
62
63
64
65
66
67 /**
68 * Pip an Object off of this Quack
69 *
70 * @return The Object
71 */
72 public Object pip()
73 {
74 Object value;
75
76
77 if (last != null)
78 {
79 value = last.value;
80 last = last.next;
81 }
82 else
83 {
84 value = null;
85 }
86 if (last == null) first = null;
87
88 return value;
89 }
90
91
92
93
94
95
96
97
98 /**
99 * Push an Object onto this Quack
100 *
101 * @param anObject The Object to push
102 */
103 public void push(Object anObject)
104 {
105 Node temp;
106
107 temp = new Node();
108
109 temp.value = anObject;
110 temp.next = last;
111
112 last = temp;
113 if (first == null) first = last;
114 }
115 }
116